Dam removal for dummies
by Nick Neely
Up and down the West Coast, people are discovering the joy of dam removal: From 2007 to 2009, 11 came down in California, nine in Oregon, and five in Washington, mainly for the sake of salmon and steelhead restoration. Here are a few pointers on dam destruction, showing the late, but little-lamented, Gold Ray Dam, near Medford, Ore. Two other dams on the Rogue River have also been removed, and another breached, in the past four years. Embark on your demolition with confidence and, please, wear a hard hat.
1 Choosing your obstacle Ideally, the dam in question is a bona fide impediment to migrating fish, as was the 360-foot-wide Gold Ray, a long-defunct hydroelectric dam. Steelhead and salmon, including threatened coho, beat themselves up climbing its outdated fish ladder and lost valuable time on their swim between the ocean and their spawning grounds. But renovating the ladder would have cost about as much as tearing the whole dam down, and Jackson County, which owned it, was eligible for a $5 million federal stimulus grant to fund most of the $5.6 million extraction. Removing the Gold Ray made this scenic river navigable again for its entire 157 miles.
2 The cardinal rule of removal To tear a dam out, you must know how to build one. Fortunately, building a temporary cofferdam is relatively easy. In June, trains hauled in loads of rock and gravel excavated from elsewhere on the Rogue. Bulldozers pushed the material into a dam behind the Gold Ray's south side, sending the river flowing over only the opposite half of the Gold Ray and forming a small pond that was later pumped dry. Now, the real fun begins.
3 Bring on the wrecking ball
- After draining the pool created by the cofferdam, use a gigantic jackhammer to drill holes near the top of the dry half of the dam.
- Insert massive steel pinchers into the ensuing gaps and mercilessly crush the concrete to rubble, from top to bedrock.
- Employ excavators to shovel the rubbish into hulking off-road vehicles. (Tip: The cofferdam might groan under their weight; be sure to monitor leaks.)
- Repeat as necessary, until half the dam is gone.
© High Country News
4 What about all that water? If the dam has created inlets, or sloughs, off the primary river channel, it's safest to drain one at a time to avoid a deluge. Fewer fish will be left high and dry this way, too. At the Gold Ray, the cofferdam joined a sandy, forested spit that divided Tolo Slough from the river channel, isolating the inlet. After half the Gold Ray was razed, workers breached part of the cofferdam. Tolo Slough drained away, taking some of the cofferdam with it. (Tip: Beware of last-minute lawsuits: A vocal few -- especially those with slough-front property -- won't be happy.)
5 Watch out for beavers Dam removal is all about adaptive demolishment. As Scott Wright of the River Design Group, an environmental consultant on the Gold Ray project, noted, removing a dam undoes "decades of stability." Be prepared. At the Gold Ray, a beaver had carved a den in Tolo Slough's spit. As the slough drained, water from the main channel flooded the beaver's tunnel, causing a leak in the spit. The spit quickly eroded, and the whole Rogue ran through Tolo Slough, weeks ahead of schedule.
6 Salvaging the fish When the Rogue River unexpectedly ran free, 333 miles of spawning tributaries became accessible. But some chinook smolt and lamprey were trapped as the reservoir dropped eight to 10 feet. The Gold Ray team jackhammered a hole in the base of the dam's still-standing north end, allowing the stranded fish to exit downstream. People with nets and buckets worked until dusk to scoop up floundering fish and tote them, swiftly, to safety.
7 Is that all? Not quite. By late August, just one triangular piece of the Gold Ray remained, looking strikingly like the fin of a giant concrete salmon beside the new river channel. Orange and yellow machines clawed at it like crawdads; soon, it was gone. Truck away all manmade debris; collect stray rebar by hand. You'll have to spearhead long-term restoration. At the Gold Ray, that will entail removing invasives like blackberry and "feral" grape, stabilizing banks, seeding dry sloughs from a helicopter, and planting trees like willow, ponderosa pine and white ash. But for now, Congratulations! Sometimes less is more.